"Curious Cook" in NY Times

PEPPERED as we are by government warnings about the potential health hazards of eating and drinking just about everything, it was refreshing (and perplexing) to see a widely respected food writer assert recently that “people are unnecessarily afraid of bacteria” in the kitchen.

But what about the harmful microbes that could grow on foods if they were not kept either chilled or hot? “Once your stock is cooked, it’s safe to eat,” Mr. Ruhlman wrote. “If there were bad bacteria in it, you’d have killed them.” After the stock has cooled, simply reheat it, he continued, and “any bacteria that landed there and began to multiply will be dispatched well before the stock hits a simmer.”

Sounds plausible, and Mr. Ruhlman and his family are alive and well. But after checking with an independent expert on food safety, I wouldn’t follow this recipe without slapping a biohazard label on my stockpot.

The Food and Drug Administration sets regulations for commercial food production. These specify that cooked foods should sit out at temperatures from 41 degrees to 135 degrees, the range in which bacteria can grow and multiply, for no more than four hours.

Guidelines for the consumer and home cook, which come from the Department of Agriculture Food Safety and Inspection Service, are even stricter. The current brochure, “Keep Food Safe! Food Safety Basics,” on the U.S.D.A. Web site, says not to leave prepared foods in the bacterial growth zone for longer than two hours. And if it’s a 90-degree summer day, cut the two hours to one.

Mr. Ruhlman’s stock spends days in the bacterial growth zone, and he happily makes it into chicken soup for his children.

I’ll admit to violating the guidelines in my own stock-making, though by a few hours, not days. When I cook a roast for dinner, I use leftover scraps and bones to start the stock, simmer it while I clean up, and take the pot off the heat right before I go to bed. At that point it’s too much trouble to cool the hot stock so it won’t warm up its neighbors in the refrigerator. Instead, I cover the pot, leave it at room temperature and reheat it in the morning, about eight hours later, before straining, cooling and refrigerating it. And my stock hasn’t made me or my family ill, either.

Can I be even more relaxed about my stock-making? Or have Mr. Ruhlman and I just been lucky? For an expert opinion, I sent our recipes to O. Peter Snyder, a food scientist and veteran educator and consultant to the food-service industry, who has at times taken issue with government guidelines he considers unnecessarily conservative.

Dr. Snyder replied in an e-mail: “The process described by Mr. Ruhlman is a very high-risk procedure. It depends totally on reheating the stock before it is used to be sure that it doesn’t make anyone ill or possibly kill them.”

It’s a basic fact that every cook should know: bacteria that cause illness inevitably end up on nearly every ingredient we cook with, and even boiling won’t kill all of them.

Boiling does kill any bacteria active at the time, including E. coli and salmonella. But a number of survivalist species of bacteria are able to form inactive seedlike spores. These dormant spores are commonly found in farmland soils, in dust, on animals and field-grown vegetables and grains. And the spores can survive boiling temperatures.

After a food is cooked and its temperature drops below 130 degrees, these spores germinate and begin to grow, multiply and produce toxins. One such spore-forming bacterium is Clostridium botulinum, which can grow in the oxygen-poor depths of a stockpot, and whose neurotoxin causes botulism.

Once they’ve germinated, bacteria multiply quickly in nourishing stock. They can double their numbers every 90 minutes at room temperature, every 15 minutes at body temperature. A single germinated spore can become 1,000 bacteria in a matter of hours, a billion in a few days.

As Dr. Snyder put it, “After sitting on the stove and growing bacteria for two or three days, Mr. Ruhlman’s stock almost certainly has high levels of infectious Clostridium perfringens cells, or Clostridium botulinum or Bacillus cereus cells and their toxins, or some combination thereof.”

Why has the Ruhlman family survived? Because Mr. Ruhlman boils the stock before he serves it, Dr. Snyder wrote. Any active bacteria are killed by holding the stock for a minute at 150 degrees or above, and botulism toxin is inactivated by 10 minutes at the boil.

But quickly reheating a contaminated stock just up to serving temperature won’t destroy its active bacteria and toxins, and the stock will make people sick.

“If Mr. Ruhlman ever has a cup of his three-day-old stock without thoroughly boiling it first, he will probably only do it once,” Dr. Snyder wrote. “It is irresponsible of any cook to prepare food in a way that actually creates a new and significant hazard, even though the hazard may be eliminated in a later step.”

Safety is one problem with keeping a stock at room temperature. Flavor is another. A reboiled three-day-old stock may be safe to eat, but it is now seasoned with millions to billions of dead bacteria and their inactivated toxins. It’s conceivable that they might add an interesting flavor, but more likely that the bacteria have feasted on the stock’s sugars and savory amino acids, the air has oxidized and staled the fat, and the stock has become less tasty.

I spoke with Mr. Ruhlman about Dr. Snyder’s analysis of his stovetop-stored stock. “I agree that I should have been clearer about the importance of the ‘kill step,’ a good 10 minutes at the boil,” he said. “And certainly to make the freshest, cleanest stock, it’s always best to strain, cool and chill it as rapidly as possible.”

What about my lazy method of letting stock cool overnight, then reboiling and refrigerating it first thing in the morning? Dr. Snyder gave it a pass because it would spend only a few hours below 135 degrees, not enough time for the bacterial spores to germinate, start growing and reach hazardous numbers.

Like meat stocks, all moist cooked foods are susceptible to being recolonized by survivalist bacteria. (Baked goods are generally too dry for bacteria; they’re spoiled by molds.) That’s why we should avoid leaving cooked foods out at room temperature for long when we’re preparing for a party or holiday feast (or enjoying their lazy follow-ups), or having a picnic, or packing lunch boxes for young children, who along with the elderly and ill are more vulnerable. It’s best to keep moist lunch items either cold or hot, surrounded by cold packs or in a thermos.

What are the actual odds of getting sick from casual food handling at home? No one really knows. There are many variables involved, and only a small fraction of illnesses are reported, even to a family doctor, since they’re usually brief. But one unambiguous and heartbreaking story can bring home the value of handling food carefully.

In 2008, a 26-year-old Japanese mother in the Osaka region shared a meal of leftover fried rice with her two children, ages 1 and 2. She had prepared and served the rice the day before and kept it at room temperature.

All three became ill 30 minutes after eating the leftovers, and were hospitalized. Both children lost consciousness, and the youngest died seven hours after the meal. Pathologists later reported in the journal Pediatrics that the rice contained a very common spore-forming bacterium, Bacillus cereus, along with a heat-resistant toxin that the bacterium tends to make on starchy foods, and that can cause vomiting even after being heated to the boil.

It may be true that most cases of food-borne illness aren’t that serious, and that most reported cases can be traced to foods that were contaminated during their production or processing. But it is also true that one simple mistake at home can be fatal.

Even though I know this, I tend to discount specific government guidelines because they seem to change arbitrarily, and they don’t seem workable in real life. This is true of the latest U.S.D.A. numbers. It’s unrealistic to expect home cooks to chill or reheat or discard dishes every two hours during a dinner party, or every hour at a summer barbecue.

Dr. Snyder agreed that official pronouncements on food safety can be inconsistent and self-defeating. “The F.D.A. Food Code is very conservatively written,” he wrote. “Four hours after it’s cooked is plenty fast enough to get food into the refrigerator.” And slow enough to relax and enjoy the meal.

Dr. Snyder added that it’s safest to cool leftovers uncovered and in a mass no thicker than two inches, so they cool through quickly. If they’re still hot, start the cooling on the countertop. When the container is no longer hot to the touch, put it in the refrigerator, and cover it once the food is good and cold.

My own everyday approach to safety is to try to keep cooked foods either hot or cold until I’m ready to serve them, get leftovers in the fridge during the pause before dessert or soon after, and reheat leftovers that need it until they’re boiling or steaming.

This set of habits isn’t dictated by an unnecessary, pleasure-killing fear of microbes. It simply acknowledges their inevitable presence in my kitchen, and the fact that both my food and anyone who eats it will be better off if the care I give it doesn’t end with the cooking.

ICED coffees and teas should be some of summer’s simplest pleasures, especially when we just steep them in cold tap water, with no kitchen heat and next to no effort. But if you make even a desultory search for advice on cold brewing, you may find yourself mopping your brow deciding how, and even whether, to proceed.

Ratios of tea or coffee to water differ wildly from recipe to recipe; brewing times can be minutes or hours. And while some respected coffee authorities praise the virtues of cold-brewed coffee, others say it’s just not as good as brewing a fresh hot cup right onto the ice.

I’ve found it calming to take a leaf from China and Japan, where one batch of tea is briefly infused as many as seven or eight times and each infusion enjoyed for its particular qualities. Variety can be just as pleasing as consistency, and it can be a way to discover new sides of our most familiar ingredients.

When we brew coffee or tea, we’re doing a very basic thing: bringing plain water into contact with dried plant materials to imbue the water with flavor, color and various active substances, like caffeine and antioxidant polyphenols. It is a basic process, but not a simple one.

As water moves into the coffee particles or tea leaves, it dissolves or suspends hundreds of different substances and extracts them from the solids. If the water is hot, it extracts more rapidly and completely. Hot water also cooks as it extracts, forcing chemical reactions that transform some of the extracted substances into other things, and driving some aroma substances out of the liquid. Cold water, in contrast, extracts more slowly and selectively, produces a simpler extract, and doesn’t change the original flavor substances as much.

So cold-brewed teas and coffees are chemically different from their hot counterparts. They tend to contain less caffeine and less acid. And, of course, they taste different. If the flavor of hot tea or coffee is your gold standard, then cold brews won’t measure up. If you think of hot and cold brews as different drinks, just as a lager isn’t the same as a pale ale, then you may find that you enjoy both.

There are a variety of specialized devices for cold-brewing coffee, including showy ones that pass water very slowly through the grounds, drop by drop, and plain functional ones in which the coffee is left to infuse in all the water overnight, then the brew drained from the grounds. The best known of these, the Toddy, is a plastic container with a thick feltlike pad that fits over a stoppered hole in its bottom. When the stopper is removed, the liquid drains through the mass of grounds and the pad, which filter out tiny coffee particles, letting a dark yet clear coffee concentrate drain into a pitcher. The concentrate can be diluted with either cold or hot water for a quick drink. Because it’s quadruple-strength, it is also handy in cooking, to flavor things like ices and ice creams.

You can improvise a cold-brewing system using a French-press pot or just a pitcher or bowl, with fine sieves, cheesecloth, or cloth or paper filters to strain out the grounds. Infuse coarsely ground coffee overnight in cold water, about 5 cups for every 1/2-pound of coffee, then press or filter the brew from the grounds. In my experience this can become tedious because fine particles clog the filters. And if you leave particles in the brew, they cloud it and give it a rougher body.

Cold-brewed coffee is controversial. To summarize the substance of many recent interviews and blog posts: advocates praise its low acidity and lack of bitterness, and its intense but smooth flavor. Detractors find it lacking in aroma and body and say they get more of both by starting with a double-strength hot pour-over or French press. The pour-over, or a Chemex brew, can be made directly over ice cubes, the French press coffee added immediately to ice. With each, the ice melts and dilutes the coffee to an appropriate drinking strength. Some automatic coffee makers now offer settings and pre-measured coffee doses for brewing strong coffee onto ice.

The hot-brew argument sounded convincing to me, and I’d be happy not to need any special kit or forethought. But when I compared a 12-hour cold brew of freshly roasted Ethiopian coffee side by side with double-strength pour-overs brewed onto ice, each was good, and it was the cold brew that consistently tasted fruitier and more refreshing. That experiment made me a fan of cold-brewed coffee. It’s certainly worth trying. Both are an improvement over simply brewing hot coffee and chilling it for hours in the refrigerator, which gives a cloudy, less flavorful drink on its own, one that benefits from mixing with milk or cream and sugar.

When it comes to tea, there’s less controversy and more flexibility. The standard proportions for American iced tea are about 4 teaspoons or 2-gram bags per quart, with a brewing time of 8 to 12 hours. In Taiwan, where cold-brewed tea has become increasingly popular in recent years and spurred studies of its chemistry, about twice that ratio of tea to water is used for a similarly long infusion. And one purveyor of fine Japanese teas in Kyoto recommends making small cups of cold sencha with 5 times that ratio, infusing first for 15 minutes, then for briefer times. The first couple of infusions are like no other version of green tea I’ve had, intensely grassy and bitter, with subsequent brews progressively milder and more refreshing.

Since cold infusion is a relatively slow and gentle process, proportions and times aren’t critical. There’s plenty of leeway for both. As a general rule, the more fragile the tea leaves, or the smaller the particles, the less tea and time you need to get a strong brew. If a cold brew infuses too slowly, just add more tea.

Two of my favorite cold-brewed teas come from Maricel Presilla, who serves a number of them at her Latin restaurant Zafra in Hoboken, N.J. One perennial on her list is a mojito iced tea, in which oolong tea scented with osmanthus flowers, or with a sliced peach and its pit, suggests the sweet aroma of white rum.

Ms. Presilla also makes an unadorned agua fresca de jamaica, the tart, deep-red sepals that surround the flower of a particular species of hibiscus.

“Nothing compares to the bright color and flavor of the cold-infused drink,” she wrote in an e-mail. “It can steep for as little as two hours and needs nothing but some sugar, though you can include spices like cinnamon, allspice or star anise for a subtle but nice flavor.”

I like to use allspice and then muddle some fresh basil in the infusion just before serving.

Jamaica (pronounced ha-MY-ka) is especially rich in antioxidant polyphenolic compounds, including its anthocyanin pigments, and food chemists are investigating its potential as a nonalcoholic alternative to red wine. They have found that a two-hour cold infusion extracts as much of the pigments as a standard hot infusion, and that the flavor is fruitier and less marked by green-leaf, clove and cooked aromas.

Less heat may mean less flavor in coffees and teas, but not necessarily less pleasure.

EVEN in kitchens where fresh is king, the freezer remains a handy tool. There’s no easier way to deal with a bounty of meat from a big-box store or a butchering class or a C.S.A. share, or the haul from a fishing trip, or the unpredictable sighting of partridge and other rare birds in the Chinese market. In my house, the freezer is essential for drawing out the enjoyment of the prime mail-order meats that my mother sends for my birthday, and that arrive rock-hard under a block of dry ice.

Less handy, however, is the thawing process, which often requires planning a day or more ahead of the cooking. Food thaws slowly in the refrigerator, especially when kept in its plastic packaging, which is the method recommended by purveyors and the Department of Agriculture to minimize bacterial growth and the loss of juices. Thawing in cold water, 40 degrees or below, is safe and much faster — water transfers heat far more efficiently than air — but it can still take hours. I’ve never had much luck with the defrost setting on microwave ovens, which can start to cook one part of the food while the rest is still frozen.

Now there’s good news for last-minute cooks. It turns out that we can thaw frozen steaks and other compact cuts in as little as 10 minutes, without compromising their quality, and with very little effort. All you need is hot water.

This information comes, surprisingly, from research sponsored by the Department of Agriculture, though the methods aren’t yet officially recommended. The studies have been published in the Journal of Food Science and in Food Control.

At the U.S.D.A. labs in Beltsville, Md., Janet S. Eastridge and Brian C. Bowker test-thawed more than 200 one-inch-thick beef strip loin steaks in three different groups: some in a refrigerator at 37 to 40 degrees Fahrenheit, some in a constantly circulating water bath at 68 degrees, and some in a water bath at 102 degrees.

Air-thawing in the refrigerator took 18 to 20 hours, while the room-temperature water bath thawed the steaks in about 20 minutes, and the hot-summer-day bath in 11 minutes. These water-bath times are so short that any bacterial growth would remain within safe limits.

The water-thawed steaks actually leaked less juice than the air-thawed steaks. The researchers grilled the steaks, too, and found that all the thawed steaks lost about 26 percent of their original weight once cooked, while never-frozen steaks lost 21 percent. The study found no significant differences in tenderness between slow- and quick-thawed steaks.

Eleven minutes is pretty quick, but Brian A. Nummer and colleagues at Utah State University in Logan shaved away another couple of minutes by heating the water bath to 140 degrees, the standard temperature of steam tables in food service kitchens.

The Utah State group found that chicken breasts about a half-inch thick thawed in a little more than 3 minutes, and inch-thick breasts in less than 9 minutes. Although 140-degree water would eventually cook the chicken to medium-rare, they saw no signs of cooking. The quick-thawed breasts did lose slightly more juice than the refrigerator-thawed breasts, but when the chicken was grilled and served, a panel of 18 tasters was unable to tell them apart. And based on their mathematical modeling, the researchers concluded that any bacterial growth would remain well within safe limits.

So there’s no downside to quick-thawing steaks, chops, fillets and other relatively thin cuts in warm water right before cooking. Large roasts are a different story. They take long enough to thaw that there may be time for significant bacterial growth on their surfaces. Prompt cooking might well eliminate that problem, but until this has been studied, it’s safest to continue thawing roasts in the refrigerator or in water under 40 degrees.

Quick-thawing is easy to adopt in the home kitchen. But don’t expect your thaw times to match the lab times I’ve quoted unless you have an immersion circulator or another method to keep the water in motion and at a constant temperature. If the water is still, a cold zone develops around the food and insulates it from the remaining warm water. And without infusions of hot water or heat from a burner, the icy food cools the water bath.

Unless I’m in a rush, I’m happy to let the thawing proceed more slowly on its own while I take care of other tasks. I fill a large pot with 125-degree water from the tap, immerse the plastic-wrapped meat, weigh it down with a slotted spoon to keep it under water and stir the water occasionally. The water temperature drops, but stays above 100 degrees for a half-hour or so, depending on how much food is thawing.

Last week, I thawed 2-inch-thick filets mignons in an hour, whole squab in 40 minutes, a 1-pound whole fish in 20 minutes, and 1 ¼-inch-thick salmon fillets in 15 minutes. Thawing times can vary, depending on the volume, temperature and movement of the water as well as the food’s thickness and how it’s wrapped. (A lot of plastic swaddling interferes with heat transfer. It’s best to remove it and place the food in a thin resealable plastic bag, partly immersing it to force the air out before zipping it shut.)

So when you scan your larder to improvise a quick meal, don’t forget to look in the freezer. The makings of the main course may be just minutes away.

WHENEVER I’m flying home and the plane passes over the south end of San Francisco Bay, my eyes can’t linger long enough over its startling patches of orange and red.

They’re sea salt ponds, cultivated to produce pure snow-white sodium chloride for industry and for the table. The colors in the ponds come from unusual microbes that thrive in the evaporating brine and produce pigments to cope with the intense sunlight.

A few months ago I finally encountered the colors of that briny life up close, in a jar of salt from the Murray River region in southeastern Australia. The remains of salt-loving bacteria and algae give the crystals a beautiful pink blush and a faint, pleasant aroma.

These days, salts come from all over the world, in many hues and crystal forms and textures. But this welcome blizzard is borne on a whirlwind of obfuscatory hype.

I’M not a big candy eater, but around the holidays I find myself longing for a few pieces of chewy Turkish delight. Despite the name and exotic rose-water flavor, it’s among the humblest of confections, made from just cornstarch and sugar. But it takes me back to the first Christmas I can remember, when the grandmother I hadn’t yet met, who was Indian and lived in England, sent me a box. For me it still carries the taste of strangeness and confusion and wonder.

I also don’t make candy very often. But when I do it seems the most magical branch of cooking, one that needs little more than plain white powder to conjure up such different marvels as glassy lollipops, opalescent ribbons, smooth creams, crumbly fudge and rich brown caramel.

WHAT'S the best oil for everyday frying? Some markets where I shop offer more than a dozen oils, from argan and avocado to tea seed and walnut. I'd long figured that the choice is a matter of taste and price. I usually use canola oil because it's neutral in flavor, a good source of omega-3s and inexpensive. Like soy oil, it costs about a dime a tablespoon, whereas extra-virgin olive oils can run well over a dollar.

Partisans of the olive maintain that a high-quality extra-virgin oil brings its special flavor and health benefits to foods cooked in it. More recipes now suggest it for frying and other high-heat techniques, not just for last-minute drizzling. But does it make enough difference that it's worth a tenfold premium in price?

ACIDS are invaluable mainstay cooking ingredients. Lemon and lime juices, myriad vinegars and sour salt, or citric acid, can brighten and balance the flavor of almost any food. But what about their chemical opposites, the un-acids? These are the alkalis, and they're a different story.

The only alkali that most cooks have ever used is baking soda. And about all we do with it is pair it with a neutralizing acid to make carbon dioxide bubbles that leaven pancakes or baked goods. We never use it as a flavoring. It's a mineral, like most alkalis, and it tastes bitter and soapy.

In fact there are a number of equally distasteful alkalis that still manage to create distinctively tasty foods, and they're becoming easier to find. Even lye, an alkali strong enough to double as a drain cleaner, is now sold online and in specialty shops in food-grade form for making pretzels.

You may draw the line at cooking with a corrosive ingredient best handled with gloves. On the other hand, baking soda is too mild to produce the particular flavors and textures that lye can. But thanks to the simplest chemical magic, you can cook up a more muscular and versatile alkali from your cupboard. You just bake the baking soda.

WHEN fine-tuning the flavor of dishes and drinks, I’ve always turned to the usual bench of taste and aroma boosters: salt and pepper, lemon juice, herbs and spices, this or that condiment. One ingredient that never, ever came to mind was water. Water has no flavor to give. It doesn’t boost, it dilutes.

Then a few months ago, the London bartender Tony Conigliaro told me that weak cocktails can be more aromatic than stronger drinks. That observation provoked me to play with the proportions of alcohol and water in spirits and wines. Then this month, a barista showed me that I could make tastier coffee by brewing it with less ground coffee and more water.

It’s true, as it turned out: Water is indeed a useful flavor enhancer, exactly because it dilutes other ingredients and can change their balance for the better.

EVERYONE knows the barbecue mantra “low and slow:” cook tough cuts of meat over low indirect heat for hours and hours until they fall off the bone and melt in the mouth.

I thought that was about all there was to it. Then I tried several recent recipes from acknowledged masters of the grill, and got dry, chewy spareribs. I took a closer look under the grill lid, and what I saw leads me to offer some fairly heterodox advice for barbecuing ribs:

WHAT do garlic and onions have in common with gunpowder? A lot. They’re incendiary. They can do harm and they delight. Sulfur is central to their powers. And they helped inspire the work of a chemist who has just published a welcome treatise on the smelly yet indispensable allium family.